.\" $OpenBSD: EVP_PKEY_get_default_digest_nid.3,v 1.9 2024/04/18 16:33:33 tb Exp $
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.Dd $Mdocdate: April 18 2024 $
.Dt EVP_PKEY_GET_DEFAULT_DIGEST_NID 3
.Os
.Sh NAME
.Nm EVP_PKEY_get_default_digest_nid
.Nd get default signature digest
.Sh SYNOPSIS
.In openssl/evp.h
.Ft int
.Fo EVP_PKEY_get_default_digest_nid
.Fa "EVP_PKEY *pkey"
.Fa "int *pnid"
.Fc
.Sh DESCRIPTION
The
.Fn EVP_PKEY_get_default_digest_nid
function sets
.Pf * Fa pnid
to the default message digest NID for the public key signature
operations associated with
.Fa pkey .
.Pp
Some signature algorithms, for example
.Dv EVP_PKEY_ED25519 ,
do not use a digest during signing.
In this case,
.Pf * Fa pnid
is set to
.Dv NID_undef .
.Pp
Support for the following public key algorithms is built into the library:
.Pp
.Bl -column -compact EVP_PKEY_base_id(3) NID_sha256 mandatory
.It Xr EVP_PKEY_base_id 3 Ta Pf * Fa pnid               Ta return value
.It Dv EVP_PKEY_DSA       Ta Dv NID_sha1                Ta mandatory
.It Dv EVP_PKEY_EC        Ta Dv NID_sha1                Ta mandatory
.It Dv EVP_PKEY_ED25519   Ta Dv NID_undef               Ta mandatory
.It Dv EVP_PKEY_HMAC      Ta Dv NID_sha1                Ta advisory
.It Dv EVP_PKEY_RSA       Ta Dv NID_sha256              Ta advisory
.El
.Sh RETURN VALUES
The
.Fn EVP_PKEY_get_default_digest_nid
function returns 1 if the message digest is advisory (that is other
digests can be used) and 2 if it is mandatory (other digests cannot be
used).
It returns 0 or a negative value for failure.
In particular, a return value of -2 indicates the operation is not
supported by the public key algorithm.
.Sh SEE ALSO
.Xr EVP_PKEY_asn1_set_ctrl 3 ,
.Xr EVP_PKEY_CTX_ctrl 3 ,
.Xr EVP_PKEY_CTX_new 3 ,
.Xr EVP_PKEY_new 3 ,
.Xr EVP_PKEY_sign 3 ,
.Xr EVP_PKEY_verify 3 ,
.Xr EVP_PKEY_verify_recover 3
.Sh HISTORY
.Fn EVP_PKEY_get_default_digest_nid
first appeared in OpenSSL 1.0.0 and has been available since
.Ox 4.9 .
